Mariah Carey had no idea she would be asked to sing when she climbed into a car with James Corden for the first carpool karaoke, his show's executive producer has revealed.

Carey was the first star to take part in the wildly successful segment of The Late Late Show with James Corden, before Adele, One Direction, Justin Bieber and most recently Britney Spears all hopped in the passenger seat.

Carey's segment has since racked up 27 million YouTube views.

Before the clips became a viral sensation they were turned down by "every publicist you can think of", Ben Winston has revealed.

Winston said their luck only turned around when he and Corden bumped into a member of Carey's team at a party and "went at her hard", showing her a clip of Corden and George Michael singing Wham! hits in a car for Comic Relief.

Winston told the Edinburgh International TV Festival: "The next day it was booked and we were shooting it. I don't know what Mariah thought but when James pressed play she was like 'We are not going to sing'".

Fortunately she eventually gamely sang along to her hits including Always Be My Baby, Vision Of Love,Thirsty, and Ol' Dirty Bastard's Fantasy,

Winston said the idea first came about when the show was thinking of segments that could be filmed in the field when stars couldn't make it to the studio and where people could sing their hits.

He said: "That is why it works, when people appear on show they usually want to sing their newest stuff, which is the last thing anybody wants to hear, but with carpool we just put their greatest hits in there.

"You can't normally ask Britney Spears to come on a show and sing ...Baby One More Time."

He said that now the three most viewed YouTube clips in the history of American late night TV are carpool karaokes.

Winston said: "I t struck a chord, it creates intimacy in such a lovely way.There are no publicists or make up artists, just James along with these people singing wonderful music. It's very joyful and it resonates."

Late Late Show clips have now amassed 1.6 billion views on YouTube in 17 months and 32 of the clips have had more that 10 million views each.

Winston promised Corden would be working on the show for years to come. He said: "I don't think he will do it forever, he won't be David Letterman doing it for 30 years but I know how long our deal is and its a fair old whack, time wise. We will be doing it for a while."